Abstract: Objective: To investigate the type of upper second molar malocclusion and its related-factors. Methods: 110 patients were randomly enrolled in this study and their models and panoramic radiographs were analyzed. The prevalence, classification and clinical manifestation of upper second molars malocclusion were analyzed. Results: The prevalence of the upper second molar malocclusion was 59.09%, and the buccoversion occupied 68.75%. There was not a significant difference between men and women. There was an inverse correlation between the widths of upper alveolar arch at upper second molar level and the upper second molars malocclusion (P=0.026). It was also found that the crowding of the buccal segment, tooth germ of upper third molar and Angle classification of malocclusion had no correlation with upper second molars malocclusion. Conclusion: The malocclusion of the upper second molars is correlated with the upper alveolar arch width at the second molar level and is not correlated with the crowding of the buccal segment, tooth germ of upper third molar and Angle classification of malocclusion. Furthermore, there is no difference between men and women.

Key words: Upper second molar, Malocclusion, Prevalence, Upper alveolar arch width